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This wait type is when a thread is calling the Windows GetDiskFreeSpace function.
(Books Online description: N/A)
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Added in SQL Server version:
Removed in SQL Server version:
Extended Events wait_type value:
The map_key value in sys.dm_xe_map_values is 453 in 2008 and 2008 R2, 501 in 2012, and 517 in 2014 RTM. After 2014 RTM, you must check the DMV to get the latest value as some map_key values have changed in later builds.
I have not seen this wait type be a noticeable contention point.
Note that when a thread calls out to Windows, the thread changes from non-preemptive (SQL Server controls the thread) to preemptive (Windows controls the thread) mode. The thread’s state will be listed as RUNNING, as SQL Server doesn’t know what Windows is doing with the thread.
Known occurrences in SQL Server (list number matches call stack list):
- Getting the volume free space (in this case, as part of performing a RESTORE DATABASE operation)
- Getting the volume free space (in this case, as part of growing the log file while adding log records)
And other similar call stacks.
Abbreviated call stacks (list number matches known occurrences list):